There are many situations in which defects in bones or portions of bones must be repaired or replaced, including fractures, joint degeneration, abnormal bone growth, infection and the like. For instance, a bone fracture may result in a crack that must be filled or in a portion of missing bone that must be replaced. Similarly, an infection may result in the removal of a portion of bone also requiring replacement.
Conventional bone replacement technologies have developed bone defect fillers for repairing bones by filling bone voids, gaps, cracks and the like. For instance, synthetic bone defect fillers, which are resorbable and porous, may replace bone with a bone-like mineral, e.g. crystalline hydroxyapatite or tricalcium phosphate. The resorbable and porous properties of these synthetic bone defect fillers allow for bone remodeling following implantation. However, conventional synthetic bone defect fillers are problematic because they may have poor tensile strength, flexural and sheer properties and they adhere poorly to the surrounding bone, which can result in washout of the bone defect filler from the bone defect prior to ingrowth of new bone into the bone defect filler.
Another conventional bone replacement technology includes bone defect fillers with a composition that maintains its chemical and mechanical properties without change or subsequent remodeling. For instance, metallic and PEEK implants may be used as interbody spacers for spinal fusion. However, these permanent bone defect fillers are problematic because, inter alia, they are not resorbable, cannot be molded and shaped for in situ curing and do not provide for adhesion with surrounding bone. Some conventional bone replacement fillers, such as PMMA, do allow for a limited amount of shaping prior to solidification. However, the time during which these conventional fillers may be shaped is relatively small, providing a surgeon with a very limited window in which the bone filler must be implanted. Additionally, like the metallic and PEEK implant described previously, these bone fillers are not resorbable and do not provide chemical adhesion between the bone and the bone defect filler.
Polymeric bone adhesives have more recently been developed for filling and/or repairing bone defects. These polymeric bone adhesives are typically initially prepared in a liquid state that is chemically adhesive. As they cure, the polymeric bone adhesives become more viscous and slowly diminish in their chemically adhesive characteristics until the polymeric bone adhesives polymerize into a final solid state. These polymeric bone adhesives may advantageously be applied to the bone defect early during the polymerization process and may be molded, shaped and allowed to cure in situ to provide both chemical and mechanical adhesion with the bone surrounding the bone defect. Thus, polymeric bone adhesives may provide improved tensile strength and adhesive characteristics over other conventional synthetic bone defect fillers. Additionally, polymeric bone adhesives may be formed with a porous structure for promoting new bone ingrowth. However, the chemically adhesive characteristics of these polymeric bone adhesives may make the polymeric bone adhesives more difficult to apply to bone defects using conventional application tools since the polymeric bone adhesives may unintentionally adhere to undesirable surfaces and/or elements contacted during handling and delivery, such as a surgeon's gloves, bone adhesive holding containers, surgical implantation instruments or the like. Additionally, if the polymeric bone adhesives are applied to the bone defect while substantially liquid, they may have a tendency to fall/run out of the application site. Care must also be taken while curing some polymeric bone adhesives to avoid contamination, which can lead to expansion, decreased adhesive characteristics and/or decreased mechanical strength.
Current solutions for handling bone adhesives include dipping the surgical gloves and/or instruments in a liquid solution, such as saline, blood or fat, prior to contact with the bone adhesive. The liquid solution is effective in reducing adhesion between the bone adhesive and the surgical gloves and/or instruments. However, the liquid solution may adversely affect the polymerization of the bone adhesive by reducing the adhesive strength at the interface between the bone and the bone adhesive within the bone defect. Additionally, the liquid solution may act as a contaminant to the bone adhesive adversely affecting the polymerization chemistry, causing excessive expansion during polymerization and/or degradation in mechanical properties by reducing the density of the bone adhesive and reducing cross-linking of polymer chains forming the bone adhesive.
Another solution for handling bone adhesives is to delay contact with the bone adhesive until the bone adhesive has partially polymerized to a degree at which its adhesiveness has lessened. However, while this technique is effective at reducing the tendency of the bone adhesive to adhere to the undesirable surfaces, such as instruments and/or gloves, it also reduces desirable adhesion between the bone adhesive and the bone surrounding the bone defect.
In some applications, bone adhesives may be applied through a syringe while in a liquid state to avoid adhesion to undesirable surfaces. However, while this technique eliminates contact with the bone adhesive, it does not allow for manipulation and/or shaping of the bone adhesive after the bone adhesive has been applied to the bone defect. Thus, the bone adhesive may lose its intended shape and/or flow out of the bone defect.
Accordingly, there is a need for a device providing improved handling, expansion and contamination characteristics for bone adhesives that overcomes the deficiencies of the prior art.